The screws are no torx screws they are Apple Pentalobe screws. You need to buy a Pentalobe screwdriver seen above.

Which MHz speed do your 8 GB modules have? If both are faster then 1333 then the Mac will not startup. I can combine a original 2 GB 1066MHz module with a 8GB 1600MHz to 10GB then the older module decides the speed and it works. But if both are the 1600MHz then the bios will not boot and I get an error signal. Will see if it could be cheaper to just get one 8GB module with 1066 or 1333 that forces the 1600 to work at lower speed.

From my experience with Sony Xperia Z2 you do not need any adhesive on the new battery,it stays in place by the other components.

I would invest in a Opening Tools

like the one from ifixit so you can open the tablet. You need to see how it looks inside to know if you can repair and how.

@cyndee Have you followed the guide above to open the tablet and looked at the battery? Can you see anything unusually? How does it look around the home button when you opened it?

Thanks for the feedback, I added the steps at least in the German Guide do not know how long it takes for the steps to show up in the translated English Version.

@Arctic W. Fox What steps are you missing?

As writen in the guide in step 2:

"If your contract has ended, you can request the code from your provider. Another way is to buy an unlock code."

Hallo moritz, bitte tausche in deiner Anleitung die Sprache in Englisch da jetzt die Deutsche Anleitung in Englisch geschrieben ist.

I have bought two screens from Honkong/Shenzen over e-bay and they where good. The next two I bought from a repairshop in Stockholm also with a good quality.